Can you set treated fence posts in cement?

Is it a good idea to set treated poles in cement? I heard it will rot fast.

Ron R. ~

Hi Ron. This is one of those questions that the answer just depends on whom you ask. I have been setting treated fence posts in cement for 30 years and have never had a problem. I also have a large workshop supported by 8-by-8 treated posts surrounded by cement that has been there for 20 years without any sign of damage or the structure weakening.

That being said, I know that some manufacturers of treated wood void their warranty if their products are set in concrete. Their recommendation is that a cement footing be poured in your hole and after it hardens the treated post is set on top. There are various types of anchoring systems available to secure the bottom of the post to the concrete. I know a lot of deck contractors use this type of system, and it seems to work well for them. If you don't want to mess with pouring concrete, you can also purchase concrete pads that can be set at the bottom of your hole to help prevent the post from sinking.

I'm more "old school" and prefer knowing that my posts are being held in place by cement rather than just soil. In either case it's important that once you have back-filled your hole, the soil allows water to flow away from the post rather than form a pocket around it. If water sits around the post where it comes out of the ground, you're eventually going to have problems regardless of whether the fence posts are set in cement or soil.

If you do decide to set your fence posts on a footing and back-fill with soil, a trick of the trade is to use small rocks mixed in with the dirt to help give the post stability. You want rocks that are about the size of the distance from the side of the post to the edge of the hole. Most digging irons have a top that resembles the head of a framing nail. If you reverse the digging iron and use the top to tamp the rocks down in, you'll be surprised at how solid your post becomes. Mix the dirt in with the rocks and make sure you do it on all four sides of the post. It's also a good idea as you work to keep checking if the post is plumb, as a large rock can cause the post to tilt.

Using this method is almost as good as using cement around the post and I have done this with long fences such as those around horse fields, where we didn't feel like using cement in every hole. That fencing was installed over 40 years ago and is still as stable as the day it was erected.